This invention relates generally to simulation for checking an automatic voltage controlled arc welder and, more particularly, to applying a simulating voltage through a linear potentiometer to an arc weld electrode to simulate changes in arc voltage as a function of electrode gap length.
Arc welding uses heat from an electric arc that discharges from a welding torch electrode across a gap to metal workpieces. Once an arc is started by either touching the electrode to the workpiece or by application of a very high voltage, the arc is sustained by application of a relatively low voltage, high current, power supply to the electrode. During welding operation, the voltage across the gap and the arc is usually on the order of 10 volts DC.
The distance from electrode-to-workpiece, or the gap spacing, is very important in arc welding because the amount of heat applied to the workpiece changes with gap spacing. If the gap is too small, the workpiece could overheat or burn through; if the gap is too large, the weld could be too cool to properly join two pieces of metal. The gap spacing is often controlled by a simple control circuit that uses the gap voltage as control voltage. If the gap voltage decreases from a desired value, the control circuit moves the electrode away from the workpiece to increase the gap spacing, thereby raising the gap voltage to the desired value.
Automatic welding operations frequently have a workpiece move relative to the electrode in a direction perpendicular to the gap. If the workpiece surface is rough, a situation which occurs when the electrode makes multiple passes over the weld joint, the control circuit senses the changes in gap voltage caused by variations in the workpiece surface and quickly moves the electrode to reset the gap voltage to the desired voltage at each point along the weld.
For any welder, it is possible to adjust the sensitivity of its control to a change in gap voltage, and the rate of feed of the workpiece relative to the gap, so the reaction of the electrode to a perturbation is predictable and repeatable. A problem may occur if the welder control system is repaired or altered. For welds after the repair that duplicate welds before the repair, the welder response to an arc voltage change must be the same after as it was before the repair. The control circuit does provide for adjustment of this response; however, a measurement of the response is necessary before a meaningful adjustment may be made. Because the arc across the gap of an arc welder is an extremely unfriendly environment for measuring apparatus, and because gap voltage is also dependent upon unpredictable factors such as the cleanliness of the workpiece and gas flow variables, accurate determination of this response prior to this invention has not been possible.